This invention relates to a mechanical press of the type used for metal stamping and forming, and more particularly to a preheat start-up arrangement and apparatus for temperature stabilization of the slide connecting rods or connection elements.
Conventional mechanical presses for metal forming or stamping include a bed which is mounted on a platform or on the floor of the shop. The bed supports a vertically spaced crown supported on a pair of uprights or vertical frame members. The crown contains a drive assembly, which typically includes a crankshaft having one or more crank means in the form of eccentrics, and connecting arms or "connections", supported at the eccentrics at their upper ends. A slide is mounted in guideways on the upright frame members for vertical reciprocating motion. The connections have lower ends which engage and support the slide at a wristpin and a threaded screw, and provide for vertical stamping movement of the slide with the rotation of the crankshaft.
A die set as used with the press has one-half mounted on the lower surface of the slide, and another half mounted on a bolster which, in turn, is mounted to the bed of the press. In precision die sets, it is important that the closing of the dies making up the set be accurately controlled, such as to less than a thousandth of an inch. In order to obtain such control to provide the proper stroke, to prevent overstroking, and to prevent or avoid tooling damage, it is necessary to bring critical parts of the press up to a predetermined operating temperature prior to press operation. Since the connections form the only link between the slide supporting one part of the die set on the one hand and the crown on the other hand, it has been found desirable to preheat the connections, for the purpose of controlling growth or lengthening in subsequent operation, and thereby substantially eliminating subsequent growth by bringing the connections up to an operating temperature prior to press operation. Further, such preheating permits the setting up of the dies to minimize the load which will be taken by the stop blocks which define the maximum die stroke, and further permits the proper setting up of the stop blocks themselves.
In the past, a heated oil circulating supply, separate from a main source of lubricating oil, has been utilized for the purpose of preheating the connections. This has entailed providing passageways through the drive shaft and the eccentrics into the connections for the circulation of heating oil therethrough, and the use of a separate heater and pump in the circuit for pumping the heated oil through the shaft, eccentrics, and connections. However, this has proven to be not only expensive, but also time consuming in that about one hour to one and one-half hours was found to be required to bring the connections up from an ambient temperature of 68.degree. F. to an operating temperature of from about 125.degree. F. to 140.degree. F.